Theoretical Analysis of Strong Changes in the Shape of Initially Elliptic Plates

On the basis of the energy approach, we obtain an analytic solution for elliptic and round plates fixed along the contour and statically loaded by uniform pressure in the case of large deflections. The numerical results are compared with the experimental data.     

复合层合矩形板水下声辐射解析计算

基于一阶剪切形变理论(FSDT),建立四边简支矩形复合层合板水下声辐射解析模型,采用一种基于定积分的方法计算板表面流载声压,以提高辐射声阻抗的运算效率。为验证算法的正确性,将所得结果与数值计算方法进行了对比。1阶剪切形变理论计算结果也与经典层合板理论(CLPT)的计算结果进行了比较,指出其在计算复合层合板声辐射时的优势。最后分析了跨厚比,铺层角度等参数对声辐射的影响,为结构噪声控制提供参考。     

Nonlinear Deflection Control of Laminated Plates Using Third-Order Shear Deformation Theory

In this paper, the third-order shear deformation theory is employed to study static and dynamic deflection control of laminated composite plates. The effects of shear deformation and geometric nonlinearity (in the von Kármán sense) on the bending and transient response are investigated using the finite element method. Magnetostrictive material, Terfenol-D, layers are used to actively control the deflection via simple negative velocity feedback control in a closed loop. The effects of the lamination scheme, types of load, and boundary conditions on the deflection are investigated.     

Photoelastic Analysis of Dynamic Stresses in Anisotropic Plates

The formulas for the correct evaluation of dynamic stresses in structurally anisotropic plates are deduced by using the polarization-optical method and the basic relations of photoelasticity. We study the wave field of stresses formed in an anisotropic plate loaded on its free boundary by pulses from a point source and the influence of anisotropy on the character of the analyzed field. The distribution of dynamic stresses induced by a concentrated source is investigated and the dependences of the maximum stresses in quasilongitudinal -waves and Rayleigh waves on the distance from the source are established.     

Dynamic Deformation of Clamped Circular Plates Subjected to Confined Blast Loading

In this paper, the dynamic deformation of thin metal circular plates subjected to confined blast loading was studied using high‐speed three‐dimensional Digital Image Correlation (3D DIC). A small‐scale confined cylinder vessel was designed for applying blast loading, in which an explosive charge was ignited to generate blast loading acting on a thin metal circular plate clamped on the end of the vessel by a cover flange. The images of the metal plates during the dynamic response were recorded by two high‐speed cameras. The 3D transient displacement fields, velocity fields, strain fields and residual deformation profiles were calculated by using 3D DIC. Some feature deformation parameters including maximum out‐of‐plane displacement, final deflection, maximum principal strain and residual principal strain were extracted, and the result was in good agreement with that simulated by AUTODYN. A dimensionless displacement was introduced to analyse the effects of plate thickness, material types and charge mass on the deflection of metal plates. DIC is also proven to be a powerful technique to measure dynamic deformation under blast loading.     

Surface Contouring of Reflecting Plates Using Intensity Integration Technique

Abstract: An intensity-based image processing method termed the Intensity Integration Technique (IIT) is proposed to obtain the slope and curvature of loaded reflecting plates. It employs divergent beam illumination to cover a large plate area. The deformation field is established by applying cumulative (integrated) intensity as the correlation parameter to relate the reflected images from the undeformed and deformed states of the object. The method is suited to modern computing environment and requires a simple experimental set-up. It obtains absolute values of slope and curvature.     

Ratcheting of 304 Stainless Steel Alloys subjected to Stress‐Controlled and mixed Stress‐ and Strain‐Controlled Conditions evaluated by Kinematic Hardening Rules

The present study predicts ratcheting response of SS304 tubular stainless steel samples using kinematic hardening rules of Ohno–Wang (O–W), Chen‐Jiao‐Kim (C–J–K) and a newly modified hardening rule under various stress‐controlled, and combined stress‐ and strain‐controlled histories. The O–W hardening rule was developed based on the critical state of dynamic recovery of backstress. The C–J–K hardening rule further developed the O–W rule to include the effect of non‐proportionality in ratcheting assessment of materials. The modified rule involved terms , and in the dynamic recovery of the Ahmadzadeh–Varvani (A–V) model to respectively track different directions under multiaxial loading, account for non‐proportionality and prevent plastic shakedown of ratcheting data over multiaxial stress cycles. The O–W model persistently overestimated ratcheting strain over the multiaxial loading paths. The C–J–K model further lowered this overprediction and improved the predicted ratcheting curves. The predicted ratcheting curves based on the modified model closely agreed with experimental data under various loading paths.     

Physico-Phenomenological Model of Metal Resistance to Plastic Deformation for the Calculation of the Processes of Metal Plastic Working. Part 2. Particular Cases of the Model and Its Experimental Validation

Particular cases of the model with reference to cold, warm, and hot deformation conditions have been considered. Parameters of the model have been determined by means of experimental stress–strain curves. For a group of low-carbon, medium-carbon, and low-alloy steels, it has been shown that the proposed model describes satisfactorily resistance to deformation in a wide temperature and strain-rate range with allowance for the effect of the loading history, which is related to the strain-rate time dependence.     

压电复合材料中III型唇形裂纹问题的解析解

采用复变函数方法和保角映射技术,研究了压电复合材料中含唇形裂纹的无限大体远场受反平面机械载荷和面内电载荷作用下的反平面问题,利用复变函数中的留数定理和Cauchy积分公式,分别获得了电不可通和电可通两种边界条件下裂纹尖端场强度因子和机械应变能释放率的解析表达式。当唇形裂纹的高度趋于零时,可得到无限大压电复合材料中Griffith裂纹的解析解。若不考虑电场作用,所得解退化为经典材料的已知结果。数值算例显示了裂纹的几何尺寸和机电载荷对机械应变能释放率的影响规律。结果表明: 唇形裂纹高度的增加会阻碍裂纹的扩展;机械载荷总是促进裂纹的扩展;电载荷对裂纹扩展的影响与裂纹面电边界条件有关。     

基于微分几何法和粒子群算法计算椭球面面轮廓度误差

基于DGA算法和误差评定的最小区域准则建立了椭球面面轮廓度误差评定的数学模型,该模型将点到椭球面的最小距离求解问题转化为一个理想椭球面球心坐标的搜索问题;采用PSO算法求取所建立数学模型的最优解。实例表明在不考虑仪器测量误差的前提下,所提出的椭球面面轮廓度误差求取方法的有效性。     

Analytical and Numerical Solution of the Stress Field and the Dynamic Stress Intensity Factors in a Cracked Plate under Sinusoidal Loading

A cracked plate subjected to a sinusoidal loading perpendicular to its plane is considered, and the analytical solution of the dynamic vibration behavior of a plate, which allowed the determination of the stress field near the crack tip, is developed. A mixed mode of loading near the crack tip has been established and described with dynamic stress intensity factors K _I (z,t) and K _II (z,t) associated with modes I and II crack openings, respectively. To validate the analytical results, a finite element analysis (FEA) of a 1 × 1 m square plate with a thickness of 1 cm, having a middle crack of 10 cm in length, is made. The results have shown significant agreement between analytical and FEA findings.     

Effect of the rheological parameters of the surface layer of structurally inhomogeneous billets on fore and strain characteristics in the case of plastic strain

On the basis of numerical simulation of the process of isothermal upsetting of a symmetric structurally inhomogeneous billet of AMg6 alloy with different rheological properties of the layers, rate sensitivity and strain-hardening coefficients of the surface layer material with fine-grained structure are determined, which ensure a considerable decrease in the level of normal contact stresses and the scalar damage parameter (degree of utilization of plasticity resource) of the article at the maximum values of contact friction factor. The possibility of using electric pulse treatment to obtain an efficient modified surface layer is substantiated. __________ Translated from Problemy Prochnosti, No. 4, pp. 123–131, July–August, 2008.     

Interaction of a penny-shaped crack with an elliptic crack under shear loading

The problem of interaction between equal coplanar elliptic cracks embedded in a homogeneous isotropic elastic medium and subjected to shear loading was solved analytically by Saha et al. (1999) International Journal of Solids and Structures 36, 619–637, using an integral equation method. In the present study the same integral equation method has been used to solve the title problem. Analytical expression for the two tangential crack opening displacement potentials have been obtained as series in terms of the crack separation parameter _i up to the order _i⁵,(i=1,2) for both the elliptic as well as penny-shaped crack. Expressions for modes II and III stress intensity factors have been given for both the cracks. The present solution may be treated as benchmark to solutions of similar problems obtained by various numerical methods developed recently. The analytical results may be used to obtain solutions for interaction between macro elliptic crack and micro penny-shaped crack or vice-versa when the cracks are subjected to shear loading and are not too close. Numerical results of the stress-intensity magnification factor has been illustrated graphically for different aspect ratios, crack sizes, crack separations, Poisson ratios and loading angles. Also the present results have been compared with the existing results of Kachanov and Laures (1989) International Journal of Fracture 41, 289–313, for equal penny-shaped cracks and illustrations have been given also for the special case of interaction between unequal penny-shaped cracks subjected to uniform shear loading.     

Multiaxial fatigue of V‐notched steel specimens: a non‐conventional application of the local energy method

The paper deals with the multi‐axial fatigue strength of notched specimens made of 39NiCrMo3 hardened and tempered steel. Circumferentially V‐notched specimens were subjected to combined tension and torsion loading, both in‐phase and out‐of‐phase, under two nominal load ratios, R=?1 and R= 0, also taking into account the influence of the biaxiality ratio, λ=τ_a/σ_a. The notch geometry of all axi‐symmetric specimens was a notch tip radius of 0.1 mm, a notch depth of 4 mm, an included V‐notch angle of 90° and a net section diameter of 12 mm. The results from multi‐axial tests are discussed together with those obtained under pure tension and pure torsion loading on plain and notched specimens. Furthermore the fracture surfaces are examined and the size of non‐propagating cracks measured from some run‐out specimens at 5 million cycles. Finally, all results are presented in terms of the local strain energy density averaged in a given control volume close to the V‐notch tip. The control volume is found to be dependent on the loading mode.     

Dynamic response of bimaterial and graded interface cracks under impact loading

The interfacial fracture in bimaterial and functionally graded material (FGM) under impact loading conditions is investigated using experimental and numerical techniques that are valid for both type of interfaces. Experiments are conducted on epoxy based specimens in three point bend configuration and the complex SIF is measured using an electrical strain gage mounted close to the crack-tip. A complementary two-dimensional finite element simulation is performed using tup force and support reactions as input tractions, and the SIF-time history is determined using a displacement extrapolation technique. The experimentally determined SIF-histories match closely with numerical simulation up to the time of fracture initiation. The test results show that the mode-mixity remains nearly constant through out the test in both the materials, and the mixity values correspond to their respective static counterparts. The general dynamic response of the bimaterial and FGM specimens in terms of impact load, support reaction and the magnitude of complex SIF are comparable, and the mode-mixity is the parameter that distinguishes the graded interface from the bimaterial case.